The is the lid and neck of a utility manhole access point. I have to add some more skins to it to allow some variety but they will all look like something akin to this:
Direct Link: http://i1265.photobucket.com/albums/jj512/WallWorm_Infidel/ManholeLid.jpg
Looking good! As with your tree model I think a normal map and some form of specular shading would do extra good on this as well to bring out the small details in the metal and brick :)